Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quantos anos o jardim de infância é legalmente exigido em Zug?
 ###Tabelas: CREATE TABLE cantonal_school_systems (cantonal_school_systems_id AUTO_INCREMENT PRIMARY KEY, Canton VARCHAR, Years of Kindergarten INT, Years of Kindergarten provided VARCHAR, Years of Kindergarten legally required VARCHAR, Length of Primary School INT, Length of mandatory Secondary School INT, Separate Secondary Schools? VARCHAR, Cooperative Secondary Schools? VARCHAR, Integrated Secondary Schools? VARCHAR) CREATE TABLE doubles_36_20–16 (doubles_36_20–16_id AUTO_INCREMENT PRIMARY KEY, Outcome VARCHAR, Date VARCHAR, Tournament VARCHAR, Surface VARCHAR, Partner VARCHAR, Opponents in the final VARCHAR, Score in the final VARCHAR) CREATE TABLE season_2:_2009-2010_weekly_ratings (season_2:_2009-2010_weekly_ratings_id AUTO_INCREMENT PRIMARY KEY, Episode VARCHAR, Air Date VARCHAR, Timeslot VARCHAR, 18-49 VARCHAR, Viewers INT) CREATE TABLE performances_results (performances_results_id AUTO_INCREMENT PRIMARY KEY, Episode VARCHAR, Theme VARCHAR, Song choice VARCHAR, Original artist VARCHAR, Order # VARCHAR, Result VARCHAR) CREATE TABLE top_25_lists (top_25_lists_id AUTO_INCREMENT PRIMARY KEY, Year INT, Performance VARCHAR, World Ranking INT, Venue VARCHAR, Date VARCHAR)  
SELECT Years of Kindergarten legally required FROM cantonal_school_systems WHERE Canton = Zug